The design of pressurized cooling air supply systems in gas turbine engines is the subject of continuous improvements, including improvements to minimize pressure losses. One location where pressure losses can occur is at the entrance of the internal cooling passages of blades between the blade retention slots and the rotor disc, referred to hereafter as a manifold.
In use, cooling air must enter the manifolds while they rotate with the rotor disk at very high speeds. Moreover, the inlets of the manifolds have a very high tangential velocity since they are located relatively far from the rotation axis. While systems are conventionally provided in gas turbine engines to induce a rotation of the cooling air before entering the manifolds, there is always a relatively large difference in the velocity of the air in front of the entrance of the manifolds and that of the periphery of the rotor disk where these manifolds are located. Air entering in a manifold must accelerate suddenly to compensate for the difference in velocities, which typically results in a tendency of generating re-circulation vortices in the manifolds. These re-circulation vortices increase pressure losses and may also, in certain conditions, prevent air from reaching one or more internal cooling passages in a blade.